The ECG is a record of the electrical activity of the heart that is a commonly used diagnostic screening test in many medical settings. The standard ECG record includes 12 lead waveforms, denoted as I, II, III, aVR, aVL, aVF, V1, V2, V3, V4, V5, and V6, arranged in a specific order that is interpreted by a physician using pattern recognition techniques. The ECG is acquired by specially trained technicians using specialized hardware and equipment. In the usual configuration, 10 electrodes are placed on the body torso to measure the electrical potentials that define the standard 12 leads. Other lead systems have been tested over the years. These include the Frank vectorcardiogram (“VCG”) system, which uses 3 nearly orthogonal leads denoted as X, Y, and Z; 4 right chest leads, denoted by V3R, V4R, V5R, and V6R; and 3 left posterior leads, denoted as V7, V8, and V9. No single manufacturer currently makes equipment that allows for the acquisition of all 22 leads. In order to acquire these leads, the technician must first remove the lead clips attached to the standard electrode placement sites and then re-attach them on the electrodes placed on the non-conventional sites. This requires at least 3 separate tracing acquisitions and a total of 21 electrode placements.
It is usual in the practice of medicine to place patients with potential cardiac abnormalities on a rhythm monitor, a specially designed hardware equipment that displays only one ECG lead but which has the capability of measuring 3 different leads. There are some manufacturers who have designed rhythm monitors that can display three leads as well but the usual display format is still one lead. With this equipment, the patient has 3 to 4 electrodes placed on the body torso to acquire the 3 different lead configurations. While the patient is connected to the rhythm monitor, if a standard 12 lead ECG is ordered, the technician will then place all of the additional electrodes for the separate acquisition of the ECG. Thus, the efficiency of acquiring an ECG would be improved if there existed a process by which the standard 12 lead ECG, the 3 lead VCG, the 4 right chest leads, or the 3 left posterior leads could be acquired instantaneously on demand from the rhythm monitor rather than the usual ECG machine, using fewer than standard number of electrodes.
Nicklas, et al., in U.S. Pat. No. 5,058,598, invented a system for synthesizing ECG leads based on developing a patient-specific transform. This system could synthesize a 12 lead ECG based on receiving data from 3 leads. However, this system required first acquiring a complete n-lead ECG from a patient in the usual manner in order to compute a patient specific transformation, which would then be applied subsequent ECG data acquired from that patient. This is cumbersome, as the resulting transformation is applicable to only one patient and needs to be stored in a medium that must be accessible for use during the patient's hospital stay. In addition, the Nicklas transformation may also have a time dependency, indicating that the patient transform may change with time such that the transformation may need to be re-computed for each subsequent encounter with that patient for diagnostic accuracy.
Dower, in U.S. Pat. No. 4,850,370, used the Frank VCG 3 lead system to derive the 12 lead ECG, however, this system is not conventional and is unfamiliar to most clinical staff. Dower also developed another unconventional lead configuration known as the EASI system, but this configuration requires the acquisition of 4 leads to derive the 12 lead ECG.